As an example of the above type of system, a vehicular steering system, which is concerned with release of the locked state, is disclosed in Japanese Patent Application Publication No. 2007-98968 (JP-A-2007-98968). In the vehicular steering system as disclosed in JP-A-2007-98968, if the absolute value of the steering torque applied to the input shaft is kept larger than a specified value for a given period of time or longer, the locked state is not released even when conditions for releasing the locked state are satisfied. It is thus possible to accurately determine a condition where a motor or drive circuit operates at a high load, and appropriately release the locked state.
According to a technology as disclosed in Japanese Patent Application Publication No. 2004-58787 (JP-A-2004-58787), when a lock release condition for releasing the locked state based on a change of the steering angle or the rate of change of the steering angle is satisfied, the locked state is released at the time when a delay time set to be longer as the temperature decreases has elapsed.
If the steering torque, when used as a criterion of determination as to release of the locked state, is temporarily reduced, such as when the driver releases the steering wheel for a moment, the locked state may be erroneously released even in the presence of a load condition that requires the locked state to be maintained. In this case, the input shaft and the output shaft are highly likely to be controlled to the locked state again, and repeatedly switch between the locked state and the unlocked or released state, whereby the driver is likely to feel uncomfortable. Namely, the vehicular steering system as disclosed in JP-A-2007-98968 has a problem that the driveability may deteriorate, in connection with release of the locked state.